Revert 163253 "Move partition page metadata out-of-line."

Speculative revert for test failures on Windows 7.
See http://src.chromium.org/viewvc/chrome?revision=239014&view=revision

> Move partition page metadata out-of-line.
> 
> There are further simplifcations to follow, but with this CL, we realize these
> benefits:
> 
> - Much less memory waste for certain common bucket sizes. The worst case is
> probably 2048 bytes which is a common allocation size and leads to a 12.5%
> wastage due to 2048 fitting perfectly in 16384 (partition page size) but us
> losing an entire 2048 byte chunk due to the 64 byte metadata header. We've
> now ditched that header.
> 
> - Complete removal of re-entrancy from the allocator. Now that the metadata is
> out-of-line, we don't lose it when freeing system pages. Therefore, we don't
> need to allocate any space for it on free. It's always there.
> 
> - Minor security improvement. It's now not possible to corrupt metadata with
> any linear buffer overflow or underflow.
> 
> BUG=324960
> 
> Review URL: https://codereview.chromium.org/99143003

TBR=cevans@chromium.org

Review URL: https://codereview.chromium.org/107603002

git-svn-id: svn://svn.chromium.org/blink/trunk@163292 bbb929c8-8fbe-4397-9dbb-9b2b20218538